Tetrahydroquinoxaline derivatives

ABSTRACT

THE PRESENT INVENTION RELATES (1) TO RUBBER PRODUCTS THAT ARE UNAFFECTED BY OZONE (2) TO ANTI-OZONANTS THAT MAY BE USED IN THE PRODUCTION OF THESE OZONE-RESISTANT RUBBER PRODUCTS, AND (3) TO THE PREPARATION OF THESE ANTIOZONANTS CORRESPONDING TO THE GENERAL FORMULA:   2-R1,3-R2,3-R3,6-R4,7-R5-1,2,3,4-TETRAHYDROQUINOXALINE

Patented May 9, 1972 US. Cl. 260-250 10 Claims ABSTRACT OF THE DISCLOSURE The present invention relates (1) to rubber products that are unaffected by ozone (2) to anti-ozonants that may be used in the production of these ozone-resistant rubber products, and (3) to the preparation of these antiozonants corresponding to the general formula:

The present invention relates to rubber products that are unaffected by ozone, to anti-ozonants that may be used in the production of these ozone-resistant rubber products and to the preparation of these anti-ozonants.

Consumer goods manufactured by vulcanisation from natural or synthetic rubber are known to develop cracks when their surface is under mechanical strain and exposed to atmospheric influences. The mechanical strain may be constant in time (static) or periodically variable (dynamic). It is known that it is the ozone present in low concentrations in the atmosphere which is responsible for the development of these cracks, and that it is primarily the choice of the elastomers used for the products in question that is of crucial importance to their resistance to this type of crack growth. For example, completely or substantially saturated elastomers such as silicone rubber or butyl rubber are highly resistant to degradation phenomena of this kind. By contrast, it is precisely these types of elastomer which are most commonly used in the rubber industry that are the most susceptible to cracking, namely natural rubber and synthetic unsaturated rubber, such as for example butadiene-styrene rubber.

We have now found that compounds corresponding to the general formula:

H t R3 R4 R3 in which R represents hydrogen or methyl,

R and R represent hydrocarbon radicals with up to 4 carbon atoms which together may also form a saturated carbocyclic ring or a methyl substituted saturated carbocyclic ring, and

R and R represent hydrogen or optionally substituted alkyl radicals with 1 to 12 carbon atoms or methoxy or ethoxy groups, one of the radicals R and R representing hydrogen when the other represents an alkyl radical with from 2 to 12 carbon atoms or a methoxy or ethoxy group,

are particularly suitable for use as anti-ozonants in natural rubber and synthetic unsaturated rubber. 4

When subjected to static testing, the rubber products protected by the compounds used in accordance with the invention show substantial advantages over those protected with compounds of the kind mentioned in French patent specification No. 1,420,036, that is to say, the beginning of crack growth is delayed to an even greater extent, whilst the growth of the cracks themselves is further retarded. 'In addition, the compounds according to the invention aso protect the rubber product against the influence of oxygen.

The compounds used in accordance with the invention may be satisfactorily incorporated in the rubber. They are used for example in quantities of from 0.1 to 5.0 parts by weight, and are preferably in quantities of from 0.5 to 3.0 parts by weight, based on the elastomer.

The anti-ozonants used in accordance with the invention may be mixed into the polymer to be protected together with the usual additives and hence also in conjunction with other anti-ozonants.

The anti-ozonants used in accordance with the invention may be employed in natural rubber and unsaturated synthetic rubbers containing double bonds, for example, in polymers of butadiene, isoprene, dimethyl butadiene and their homologues, also in copolymers of conjugated diolefins with polymerisable vinyl compounds such as, for example, styrene, methyl styrene, divinyl benzene, acrylonitrile, methacrylonitrile, acrylates or methacrylates, and in copolymers obtained from isoolefins, such as isobutylene or its homologues, and small quantities of conjugated diolefins. It is also possible to protect polymers of the kind obtained from chlorobutadiene, and also copolymers of chlorobutadiene with mono and/ or diolefins or polymerisable vinyl compounds.

Table 1 contains examples of the compounds used in accordance with the invention:

TABLE 1 3,3-dimethyl-l,2,3,4-tetrahydroquinoxaline; 3,3,6- or 3,3,7-trimethyl-l,2,3,4-tetrahydroquinoxaline; 2,3,3-trimethyll ,2,3,4-tetrahydroquinoxaline; 2,3,3,6- or 2,3,3,7-tetramethyl-l,2,3,4-tetrahydroquinox aline; 2,3,3,5-tetramethyl-1,2,3,4-tetrahydroquinoxaline; 2,3,3,5,7-pentamethyl-1,2,3,4-tetrahydroquinoxaline; 3-ethyl-3-n-butyl-l,2,3,4-tetrahydroquinoxaline; 3-ethyl-3-n-butyl-6- or 3-ethyl-3-n-butyl-7-methyl-l,2,3,4-

tetrahydroquinoxaline; 3-spirocyclohexyl-1,2,3,4-tetrahydroquinoxaline; 3-spirocyclohexyl-6- or 3-spirocyclohexyl-7-methyll ,2, 3 ,4-tetrahydroquinoxaline; Z-methyl-3-spirocyclohexyl-l,2,3,4-tetrahydroquinoxaline; 3,3-dimethyl-6- or 3,3-dimethyl-7-tert.-butyl-1,2,31,4-

tetrahydroquinoxaline; 3,3-dimethyl-6- or 3,3-dimethyl-7-i-nonyl-1,2,3,4-tetrahydroquinoxaline;

3,3-dimethyl-6- or 3,3-dimethyl-7-tert.-dodecyl-l,2,3,4-

tetrahydroquinoxaline;

3,3-dimethyl-6- or 3,3-dimethyl-7-methoxy-l,2,3,4-tetra hydroquinoxaline; and

3,3-dimethyl-6- or 3,3-dimethyl-7-ethoxy-1,2,3,4-tetrahydroquinoxaline.

The compounds used in accordance with the invention may be obtained by condensing o-phenylene diamincs 4 With corresponding a-halogen ketones to form dihydroand Raney nickel, Raney cobalt and nickel on supporting quinoxalines, followed by catalytic reduction: materials.

NH H Hcl CH NaOH CH i CH We have also found that the optionally substituted 3,3- The following 2 -alkylamino-2,3-dihydro-3,3-dialkyldialkyl-tetrahydroquinoxalines can 'be obtained by hydroquinoxaline-di-N-oxides are mentioned as examples of genating optionally substituted 2-alkylamino-3,3-dia1kylstarting materials for this process:

dihydroquinoxaline-di-N-oxides initially at temperatures around room temperature (for example, from C. to C.), and then splitting off the amine radical through reduction by continuing hydrogenation at elevated temperature, i.e., at temperatures of from approximately 60 1 h J 1 th th c. to 200 c. The 3,3-dialkyl-tetrahydroquinoxalines that 353 23 2338 lfifi gjf are otherwise impossible or extremely difficult to obtain 25 z cyclohexylamino 33 dimethy1 6 or are formed in this way. 2411GT th The course followed by the reaction is illustrated by p m lme y d -3,3-d' th 1- the followmg reaction scheme: gggig g g ifig g i 2-methylamino-3,3-dimethyl-,

20 2-ethylamino-3,3-dimethyl-,

2-cyclohexylamino-3,3-dimethyl-, 2-cyclohexylamino-3,3-dimethyl-6- or -7-methyl,

1f 1t 3 R R 4 a n n /ar. 2 R R R a R ma e In the above formulae, R and R represent hydrogen 2-cyclohexylamino-3,3-dimethy1-, or optionally substituted alkyl radicals with 1 to 12 car- 2cycloheXylamino-3,3-dimethyl-6- or -7-methyl-, bon atoms or methoxy or ethoxy groups, one of the radi- 2-cyc1 heXylamino-3,3-dirnethyl-6- or -7-meth0xy-, cals R and R representing hydrogen when the other -cyc10heXylamino-3,3-dimethyl-6- or -7-ethoxy-, represents an alkyl radical with from 2 to 12 carbon l-cyclohexylamino-3-spifo-cyclohexenyl', atoms or a methoxy or ethoxy group, R represents hy- Y Y p y y y drogen or lower alkyl, R represents hydrogen or alkyl Y radicals, and R represents alkyl or cyclo-alkyl radicals, P y Y' y and in addition R and R may optionally form together 2'cyclbhexylamlno'zmethyl-3,3-d1methY1- and D P a ring which may contain another hetero atom such as q f y P Y 0f Y- 3- N, S or 0, Whilst R and R represent an alkyl radical dlhydroqulnoxalme'dl-N-oXldemay be joined togbthel: to form carbbcyclic i The following are mentioned as examples of com- WhlCh may optionally contain methyl groups and WhlCh pounds th t can be prepared by this process:

in the starting material may also contain a double bond. The radicals R and R may for example contain 1 to 12 33'dlmethyl'1234'tetrahydroqumoxahne carbon atoms, whilst the radical R is preferably a lower or alkyl radical with up to 4 carbon atoms. qulnoxaline The alkyl radicals R and R may contain, for example, 3 f or from 1 to 12 carbon atoms and may be substituted by qumoxahne further radicals, for example, by lower alkoxy radicals i f or '7 ethoxy 12'34'tetrahydm' such as methoxy, ethoxy or propoxy radicals, or a halogen qumoxa such as chlorine. Reduction may be carried out in the 0 g ig i ggg ig i i; i i fg g usual way in solvents such as alcohols and ethers, esmg y lme y or met y A'mtra' hydroquinoxaline pecially methanol and tetrahydrofuran. 1 h 1- 4- In the first stage of reduction, the oxygens of the N- Dim-WC o exy L2 tetrahydloqumoxahne 3-s iro-c clohex 1-6- or -7-meth l-1,2-3,4-tetrah d oxide groups are removed by reduction at temperatures gumogaline, y y y to of for example from to Preferably 3-spiro-cyclohexyl-6- or -7-ethoxy-l,2-3,4-tetrahydrofrom 10 C. to 30 C. The reaction is then completed quinoxaline,

at elevated temperatures, for example, at temperatures 3-spiro-methylcyclohexyl-1,2-3,4-tetrahydroquinoxaline,

of from 60 C. to 200 C. and preferably at temperatures and of from C. to 150 C., accompanied by elimination 70 3-spiro-methylcyclohexyl-6- or -7-methyl-1,2-3,4-tetra- 0f the amine radical through reduction. hydroquinoxaline- The l'eactlon Products may be Worked P y precipim" The 2 alkylamino 3,3 dialkyldihydroquinoxaline-ditlon Wlth Water y distilling the compounds formed N-oxides used as starting materials can be obtained by Examples of the reduction catalysts for the process reacting benzofuroxanes with ketimines or enamines. The

include both noble metals such as platinum and palladium course followed by the reaction of methyl-benzofuroxane with e.g. N-cyclohexyl-l-methyl-2,2-dimethyl-ketimine is illustrated by the following reaction scheme:

The resulting final product is a mixture of 2-cyclohexylamino-2-methyl-3,3-dimethyl-6- and -7-methyl-2,3-dihydroquinoxaline-di-N-oxide due to one methyl group being substituent of the benzo nucleus. The 6-position isomer appears to be the main product in all cases where the benzofuroxane used in this reduction carries one substituent.

The invention is illustrated by the following examples:

EXAMPLE 1 The following mixtures suitable for use in the treads of vehicle tyres were prepared on laboratory mixing rolls:

Parts by weight Oil-extended styrene butadiene rubber (37.5 parts by weight of oil to 100.0 parts by weight of Test specimens measuring 0.4 x 4.5 x 4.5 cm. and 0.4 x 4.5 x 5.5 cm. were prepared from these mixtures and vulcanised in a press for 30 minutes at 151 C. The test specimens were then clamped in a plastics frame in such a way that elongations of 10, 20, 35 and 60% were produced over their surface. The test specimens thus bent were weathered without any cover in a southerly direction. Crack growth was assessed at certain intervals as specified in the following table on the basis on the total number of cracks visible with the naked eye and also their average length in accordance with the following scheme:

In the following tables, the results of the two assessments are separated by an oblique line, the number of cracks being shown first in each case.

(a) No addition:

Evaluation after- Elongation (percent) 0 days 7 days 14 days 21 days 28 days 42 days (b) 2.0 parts by weight of 2,3,6- or -7-trimethyl-l,2,3, 4-tetrahydroquinoxaline from French Pat. No. 1,420,036 (by way of comparison):

Evaluation after- Elongation (percent) 0 days 7 days 14 days 21 days 28 days 42 days (c) 2.0 parts by weight of 3,3,6- or -7-trimethyl-1,2,3, 4-tetrahydroquinoxaline Evaluation after- Elongation (percent) 0 days 7 days 14 days 21 days 28 days 42 days (d) 2.0 parts by weight of 3,3-dimethyl-1,2,3,4-tetrahydroquinoxaline Evaluation after- Elongation (percent) 0 days 7 days 14 days 21 days 28 days 42 days (e) 2.0 parts by weight of 3-spiro-cyclohexyl-6- or -7-methyl-1,2,3 ,4-tetrahydroquinoxaline (15) 2.0 parts by weight of 2,3,3,6- or -7-tetramethyl- 1,2,3,4-tetrahydroquinoxaline:

Evaluation after Elongation (percent) 0 days 7 days 14 days 21 days 28 days 42 days (g) 2.0 parts by weight of 2,3,3-trimethyl-l,2,3,4-tetrahydroquinoxaline Parts by weight Smoked sheets 100.0 ISAF carbon black 48.0 Zinc oxide 5.0 Mineral oil plasticiser 4.0 Stearic acid 3.0 Paralfin 0.6 Sulphur 2.2 2-benzthiazyl-N-cyclohexyl sulphenamide 0.6 Anti-ozonant (see below) 0 and 2.0

As described in Example 1, test specimens were prepared from these mixtures and vulcanised in a press for 25 minutes at 143 C. The test conditions were again the same as in Example 1. Similarly, crack growth was assessed as in Example 1.

hydroquinoxaline:

Evaluation after- Elongation (percent) days 7 days 14 days 21 days 28 days 42 days (c) 2.0 parts by Weight of 3,3,6- or -7-trirnethyl-1,2,3, 4-tetrahydroquinoxaline Evaluation aite1'- 8 EXAMPLE 3 3,3-dimethyl-6- or -7-methyl tetrahydroquinoxaline (I) 630 g. (2.80 mols) of a mixture of 2-cyclohexylamino- 3,3-dimethy1-6- and -7-methydihydroquinoxaline di N- oxide are introduced together with 120 g. of Raney nickel into 2.5 litres of methanol and hydrogenated in an autoclave at 25 C. After the hydrogen has been absorbed, the temperature is increased to 100 C. and hydrogenation is completed at 150 C. After the catalyst has been filtered off and the solvent distilled off together with cyclohexylamine formed, the residue is distilled 270 g. of B.P. 115-125 C. are obtained. The distillate solidifies and melts at 59 C. to 60 C. after dissolution in and reprecipitation from petrol.

Analysis.-C H N (176). Calculated (percent): N, 15.92. Found (percent): N, 15.9.

The product obtained is a mixture consisting of 3,3-di- Elon ation erc em Odays 7days 14 days 21 days 28days 120 hyl 6 methyl tetrahydroqumoxahne and 3.3 dimethyl 0 7-methyl-tetrahydroqu1noxal1ne. The mixture is separated g 82g (9% Egg (83% gig.) gzg into cilts 132/0 ctonstiglentsb 1by chromatlogrlaphg The 0111- 00 poun s se en mi e ta e were sim'ary o tained rom 1. 4 1. W0 0/0 0/0 4/1 4/ 5 l 5 25 the corresponding starting materials:

Analysis Calculated Found Yield in B M.P. percent of Number Formula -P C H N O H N theoretical 11 g CH3 44-45 74.0 8.64 17.20 79.9 8.7 17.1 49.0

III H CH 0. 41130-133 68.7 8.33 14.56 68.7 8.8 14.4 64.5

N 3 CHa CH3O CH, H

v 1 3 CH; 58-60 74.9 9.1 15.9 75.1 9.2 15.9 43

H g CH v H CH 37-38 75.8 9.48 14.73 70.0 9.5 15.0 70.5

N 3 orn- -C-H3 g CH;

on, on;

CH1- H g on,

VI g CH3 0.9/132-137 70.9 9.0 12.73 71.0 9.3 12.5 3

CH3 L The starting material required for the preparation of IV is obtained as follows:

85.5 g. of benzofuroxan and 105 g. of N-cyclohexyl-lmethyl-2,2-dimethyl ketimine (Schiifs base of cyclohexylamine and methyl isopropylketone) are introduced while stirring into 400 m1. of methanol. There is a rise in temperature to 25 C., accompanied by dissolution. 100 g. of 2-cyclohexylamino-Z-methyl 3,3 dimethyl-dihydroquinoxaline-di-N-oxide crystallised out over a period of 12 hours. After dissolution in and reprecipitation from methanol, the red crystals melt at 129-131 C.

I on, CH3

CH3 a Calculated (percent): C, 67.2; H, 8.31; N, 13.95. Found (percent): C, 67.2;H, 8.6; N, 13.95.

The starting materials for V and VI are similarly obtained with the correspondingly substituted benzofuroxans:

0 I CH3 CH CH;

CH; r

M.P. 147-148" C. red crystals CH3 m CzHso CH a M.P. 128130 C. red crystals EXAMPLE 4 (a) 36 g. (0.3 mol) of 2-chloro-2-methyl-3-butanone are introduced into a suspension of 33 g. (0.3 mol) of o-phenylene diamine in 150 ml. of methanol, and the resulting product is heated to boiling point over a period of 4 hours. It is then cooled, 20 ml. of a 45% aqueous NaOH solution and 150 ml. of water are added, and the deposit precipitated is suction-filtered and Washed with methanol/water in a ratio by volume of 1:1. 2,3,3- trimethyl-3,4-dihydroquinoxaline is obtained in a yield of 39 g. (75% of the theoretical) in the form of beigecoloured crystals which melt at 143148 C. following dissolution in, and reprecipitation from, benzene/light petrol.

Analysis.C H N (174.2). Calculated (percent): C, 75.8; H, 8.1; N, 16.1. Found (percent): C, 75.7; H, 8.2; N, 16.1.

(b) 20 g. of Raney nickel B are added to a solution of 61 g. of 2,3,3-trimethyl-3,4-dihydroquinoxaline in 300 m1. of tetrahydrofuran, and the resulting product is reduced with hydrogen in an autoclave at 110 C. The catalyst is then filtered off, the solvent is distilled off in vacuo and the oily residue is dissolved in light petrol. After standing for a limited period, crystals are precipitated, being filtered under suction and washed with light petrol. 2,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline is obtained in a yield of 30 g. in the form of yellowish crystals melting at 65 C. to 67 C.

The product is identical with 2,3,3-trimethyl-1,2,3,4- tetrahydroquinoxaline (substance No. III) prepared in accordance with Example 3.

10 What we claim is: 1. A compound corresponding to the formula in which R represents hydrogen or methyl, R and R represent hydrocarbon radicals with up to 4 carbon atoms which may also be attached to one another to form a 6 membered saturated carbocyclic ring which may be substituted by methyl groups, and R and R represent hydrogen or alkyl radicals with l to 12 carbon atoms or methoxy or ethoxy groups, one of the radicals R and R representing hydrogen when the other represents an alkyl radical with from 2 to 12. carbon atoms or a methoxy or ethoxy group.

2. The compound of claim 1 having the formula CH CH3 3. The compound of claim 1 having the formula E CH 0H,- Ion,

H g CH3 4. The compound of claim 1 having the formula CH3 0/ V CH3 H g CH 5. The compound of claim 1 having the formula CH3 CH3 H g CH3 6. The compound of claim 1 having the formula CH N CH5 0211 0 \N OH:

7. The compound of claim 1 having the formula H on N 3 our H 8. The compound of claim 1 having the formula 9. The compound of claim 1 having the formula 10. Process for the production of a compound corresponding to the formula in which in which R R R R and R have the meaning given above,

R denotes hydrogen or an alkyl radical and R represents an alkyl or cycloalkyl radical, and in addi tion R and R may also form a ring which may contain another heteroatom being N, S or O initially at temperatures of from -20 C. to 40 C. and thereafter eliminating the amine radical of the formula in which R and R have the meaning given above, by continuing hydrogenation at temperatures of from approximately 60 C. to 200 C.

References Cited UNITED STATES PATENTS 3,291,757 12/1966 Sturm et a1. 260-250 R NICHOLAS S. RIZZO, Primary Examiner US. Cl. X.R. 260-45.8 A 

